Method of producing tungsten



Patented May 29, 1951 METHOD ,OF PBQDUCINGJIUNGS'IEN Colin G. Fink and ChulcChingcMa, New'York, N. Y.

.N Drawing- Ori in l p li at on 'E brua rj 1944; SerialNo. 523,092. D ivjded andthis application July 29, -1948, Serial No. 41,400

. 2 'Glaims. ((01. 204 64) 'This invention-relates to the recovery of metallic tungstenfrom tungsten compounds; tungsten ores and concentrates of tungsten ores. More specifically, the invention provides an electrolytic method for the direct production of crystalline grains of substantially pure metallic tungsten from compounds, ores, and ore concentrates'of tungsten. This application is a division of our rent efficiency. In 1931, Hartmann et al. (Zeitschr. Anorg; Chemwol. 198, p. 116) described a-method of producing metallic tungsten electrolyticallyirom a fused mixture of sodium pyroapplication Serial No. 523 092, filed February 19, Y

1944, now Patent Number 2,463,367, issued March 1; 1949.

Tungsten occupies a position of major importance among industrialmetals, owing to its widespread use not only as lamp filaments but also as a constituent of alloy steels, of cutting tools, of

Y 5 phosphate and metaphosphate with tungstic acid,

at :650-700' C., and also from a solutionof tungstic oxide in sodium pyrophosphate. This process-was further investigated by Leo and Shen (Trans. Electrochem. Soc. vol. 66, p. 461).

Itwillbe noted that all of these prior investigators used eithertungstic oxide or sodium tungstate, a water-soluble salt. Apparently, none considered his method applicable to impure tungstenmaterials such as ores or concentrates. In-

15.-. asmuch as relatively expensive procedures are redies, and other articles which must resist abrasion or be strong at high temperatures.

The commercially important ores of tungsten are scheelite (calcium tungstate) and wolf-ram'ite,

an iron-manganese tungstate of which two common variants are the iron-rich ferberite and the manganese-rich huebnerite. 'These ores are usually concentrated by hand or mechanically although recently chemical extraction methods have been developed for leaching lean ores of tungsten and producing concentrates in the form of pure or nearly pure calcium or sodium tungstate. The concentrates,..however produced, are ordinarily either smelted in the electric furnace to produce a ferrotungsten alloy, or,purified and converted to tungstic, oxide which is, then reduced with carbon or hydrogen to pure or nearly pure tungsten metal.

It has been proposed to produce metallic tungsten by electrolytic reduction ,of .tungstencom-g pounds. Inv 1867' Zettnow (Pogg. Ann. vol. 130, pages 16 and 24 1) described the production of impu tu te p n el c ro is of. sodium tungstate. v In 1919 v Keyes patented (Patent ductionoof amorphous tungsten, powder by elec.-.-

trolyzing alkali metal tungstates. In .1929 Andrieux (Ann. Chim. vol. 12, page 495; Comptes Rend. vol. 184, page 91) having found that fused mixtures of tungstic and boric anhydrides form very viscous baths having poor conductivity,.de-

scribed the production of a crystalline tungsten powder by electrolyzing a fusedmixture oi tungstic oxide; borates, and. fluorides. Andrieux considered the; further: adliiticnxof zinc,-.oxide tc-be quired to produce pure tungstic oxide or sodium tungstate from tungsten ores, these electrolytic reduction methods ofier' little or no cost advantage over other reduction methods in producing tung- 1 sten, particularly when it is considered that prior workerswere able to operate only at low current elficicncies and were unable. to prevent the simultaneous. production of large amounts of compounds of lower oxides of tungsten or tungsten bronze. Largely for these reasons, production of tungsten metal by electrolysis has not attained commercial acceptance.

, It has :now been discovered that tungsten ores and concentrates such as wolframite, ferberite, huebnerite, and scheelite, preferably in finely granular form, may be readily dissolved-in molten alkaliphos-phates, and'that under certain conditions described hereinafter the solutions may be electrolyzed to produce substantially pure, crystalline tungsten metal grains.

More specifically, the; invention comprises mixing a tungsten ore or a tungsten ore concentrate with at leas-tone molten solvent salt selected from the group consisting 'of sodium pyrophosphate (NazPzO and mixtures of sodium pyrophosphateixwith sodium -:metaphosphate (NaPOa), maintaining the solution .so obtained at a temperature. between 950 and .1300 C., andelectrolyzingsaid hot solution between an anode and a cathode-at .a cathodecurrent density between 2 and 4 amperes per square inch. Neither fluorides-,nor 'zinc oxides are .usedin the salt bath.

It is preferred that the initial proportions of ingredients be such that there are between 1.5

50. and 3.5 parts of solvent to each part by weight ofgtungstic oxide (although as much as '7 par-ts of solvent to 1 part of tungstic oxide may be used), and it also'preferred that the proportions be-.-maint,ainedwith-in these limits throughout thecelectrolysis. Gangue constituents may becloud. the solution but such cloudiness does not interfere with the process.

rifestsyhave established that'the solvent sodium salts -may be replaced. wholly'.-.or in part by the necessary to QbtainaPH- QWHB'SEQHat 81; hi hcuncrresaond-ina. potassium salts without-substanbut is preferably of about the same order'as that at the cathode.

The cathode may be made of any suitable conductive material, such as ironor graphite; but is preferably of molybdenum or tungsten. Graphite is the preferred anode material.

The process steps and conditions just described are critical if a pure product is to be obtained under efiicient operating conditions. Thus, baths initially containing less than about 28%, or more than about 67% by weight of tungstic oxide are electrolyzed only at very low current efficiency.

The temperature and the current density exert strong efiects not only on the current efficiency but also on the purity of the product. It seems most probable, on the basis of extensive data accumulated in the course of investigation of this process, that a film of sodium vapor is formed on the cathode, that for optimum results in respect.

to current efiiciency and purity of product there is a narrow range of optimum thicknesses of such film, and that the most significant of the factors controlling such film thickness are the temperature of the electrolyte and the current density at the cathode. I 1

There is a very sharp enhancement of current eificiency as the electrolyte temperature is raised from 950 to 1025 C. A further increase in temperature is accompanied by a much less rapid increase in current efiiciency, until a maximum is reached in the range of 1050 to 1150 C., after which, at higher temperatures, the efficiency decreases, again reaching a low value at about 1300-1350 C.

Similarly, current efficiency is at a maximum when the current density at the cathode is in the neighborhood of 3 amperes per square inch, and reaches a low value at densities below 1.5 and above 4 amperes per square inch. The greatest purity of product, i. e. greatest freedom from tungsten bronzes, is achieved at current densities above 2.5 amperes per square inch.

In a series of experiments using wolframite concentrates dissolved in fused phosphates, best results were obtained under the following conditions: as the initial electrolyte composition, one part by weight of ore concentrate (60 %-'70% W03) in each one and three-quarters part of fused phosphate mixture; a phosphate mixture in the proportion of seven mols sodium pyrophosphate to three mols sodium metaphosphate; electrolyte temperature between 1050 and'1300" C.;

current density at the cathode, about 50 amperes per square decimeter (3.23 amp/sq. in.). Under these conditions, current efficiencies of about 80%, yields of about 1.12 pound per kilowatthour, and a product analyzing 99.7% tungsten, have been achieved.

The tungsten metal, as it is formed, usually drops to the bottom of the electrolyte bath where it forms a sludge which is readily separated from the main body of the electrolyte by decantation. If a hollow molybdenum cathode is used, tungsten crystals will adhere to it. The sludge also con tains various impurities such as compounds of lower oxides of tungsten. After the sludge has been cooled and solidified, the pure tungsten is easilyv separated by leaching. The metal itself is.

4 substantially free from those impurities such as phosphorus, arsenic, sulfur,'and tin, which are commonly present in tungsten ores but which impair the value of tungsten metal for use in steels.

The process may be applied not only to high grade ore concentrates but also to low grade ores and concentrates, with some decrease in current .efiiciencysomewhat better current eiiiciencies have' been attained with the use of wolframite,

ferberite, and huebnerite than with scheelite, but .verygood results are achieved even with scheelite'.

In general, within the ranges of conditions specified herein, raising the current density tends to yield smaller crystals of tungsten, while raising the temperature tends to yield larger crystals. Insoluble impurities, such as iron oxide, also afiect the crystal size, an increased concentration of such impurities tending to decrease the crystal size.

I What is claimed is:

1. Method of producing substantially puretungsten crystalline grains directly from ganguecontaining oxidic tungsten ores and gangue-containing .concentrates thereof which consists of mixing said tungsten-containing material with a molten solvent salt selected from the group consisting of sodium pyrophosphate and mixtures of sodium pyrophosphate with sodium metaphosphate, said tungsten-containing material providing tungstic oxide in amount from 28% to 67% of the mixture; maintaining the gangue-containing solution so obtained at a temperature between l025 and 1300 C.; and electrolyzing, at such temperature, said hot solution as an electrolyte between an anode and a cathode at a cathode current density between 2 and 4 amperes per square inch.

2. Method of producing substantially pure tungsten crystalline grains directly from ganguecontaining oxidic tungsten ores and gangue-containing concentrates thereof which consists of mixing said tungsten-containing material withv COLIN G. FINK. CI-IUK CHING MA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Cobb July 14, 1925 OTHER REFERENCES Leo et al., Transactions of the Electrochemical Society, vol. 66, pages 461-469 (1934) Production of the Heavy Metals by the Fused- Electrolyte Method II Production of Iron, Chromiumand Manganese from Oxides and silicates.

Number v C:r. Nuendorff and F. SauerWald, Zietschrift fiir 'Elektrochemie-M, 199-204 (1928). 

1. METHOD OF PRODUCING SUBSTANTIALLY PURE TUNGSTEN CRYSTALLINE GRAINS DIRECTLY FROM GANGUECONTAINING OXIDIC TUNGSTEN ORES AND GANGUE-CONTAINING CONCENTRATES THEREOF WHICH CONSISTS OF MIXING SAID TUNGSTEN-CONTAINING MATERIAL WITH A MOLTEN SOLVENT SALT SELECTED FROM THE GROUP CONSISTING OF SODIUM PYROPHOSPHATE AND MIXTURES OF SODIUM PYROPHOSPHATE WITH SODIUM METAPHOSPHATE, SAID TUNGSTEN-CONTAINING MATERIAL PROVIDING TUNGSTIC OXIDE IN AMOUNT FROM 28% TO 67% OF THE MIXTURE; MAINTAINING THE GANGUE-CONTAINING SOLUTION SO OBTAINED AT A TEMPERATURE BETWEEN 1025* AND 1300* C.; AND ELECTROLYZING, AT SUCH TEMPERATURE, SAID HOT SOLUTION AS AN ELECTROLYTE BETWEEN AN ANODE AND A CATHODE AT A CATHODE CURRENT DENSITY BETWEEN 2 AND 4 AMPERES PER SQUARE INCH. 